1. Field of the Invention
The present invention relates to a vehicle with a power unit, and more particularly to such a vehicle having a suspension capable of preventing engine vibration from being propagated from the power unit to a vehicle frame.
2. Description of Relevant Art
There are known two- and three-wheeled motorcycles having a power unit composed of an engine and a transmission case, which is suspended from a vehicle frame through a linkage mechanism and a damper or cushioning unit. One known way of reducing engine vibration transmitted from the power unit to the vehicle frame has been to apply primary engine vibratory forces in the direction in which the link swings, as disclosed in Japanese Patent Publication No. 38-12215. However, there has still been a demand for a larger reduction of the engine vibration transmitted to the vehicle frame, especially from power units having a larger cylinder volume or piston displacement and an increased weight.
Another drawback associated with known two- and three-wheeled motorcycles is that the transmission case is disposed on one side of the rear wheel, so that the center of gravity of the power unit is displaced, as seen from above the vehicle, transversely of the vehicle from the center where primary vibratory forces of the engine are produced. With the center of gravity of the power unit being thus displaced, the power unit is subject to rotational vibration around its vertical axis. Such rotational vibration becomes larger as the center of gravity of the power unit is displaced to a larger extent. The rotational vibration acts as a couple of forces on the link interconnecting the power unit and the vehicle frame, and hence is propagated to the vehicle frame.